The invention relates to a process and an apparatus for sinking drill holes, in particular for exploration and extraction and drill holes.
Exploration drill holes are made for the purpose of prospecting deposits and should permit the taking of samples of the material present in the deposit. Exploration drill holes are sunk, in particular, when the deposit is located at great depth and/or when water that is present above the deposit, e.g. an ocean or sea, does not permit the sinking of exploration shafts.
Extraction drill holes serve to extract the deposit content from bottom layers. An example of extraction drill holes is the mining of marine sediments with diamond inclusions present on the ocean floor.
The deposits containing the diamonds have generally been formed in front of river mouths in the form of not very thick layers spread out on a rock base. To mine the diamond-containing sediment material, apparatuses are used which are lowered onto the ocean floor from ships on an extendible drill-pipe. Such apparatuses may have drill heads which are designed for drill holes with a large diameter. Several such drill holes are made close to one another so as to be able to extract as much as possible of the diamond containing material.
When the drill head fastened to a drill-pipe which may have a great length encounters the ocean floor, the problem occurs that at the place on the ocean floor where the drill hole is to be made, the drill head of the drilling tool does not penetrate immediately, but tends to slip and move around spiral-shaped in a circle, especially when the ocean floor has even the slightest slope.
To prevent this slipping sideways of the drill head, it is already known to arrange a centering guide point underneath the drill head, which under the drilling force exerted in the operating direction of the drill head penetrates into the surface of the sediment layer and, in particular in the initial phase of the drilling, provides a guidance that prevents a slipping sideways of the drill head at the start of the drilling operation, i.e. when the drill head is not yet guided at is sides by the drill hole walls.
When the drill head has passed nearly completely through the sediment layer, the projecting guide point is the first to encounter the generally rocky base located underneath, into which it cannot penetrate or only very slowly and with great wear. The drill head than cannot penetrate further into the sediment layer.
As the profitability of the extraction process depends on the quick sinking of a large number of adjacent drill holes, the respective drilling operation until now is greatly delayed when the guide point encounters the bedrock located underneath the sediment, and accordingly becomes uneconomical.
From the U.S. Pat. No. 3,277,972 an apparatus is known with which the drill head is moved down during the penetrating into a soft sediment layer. The drill head is arranged movable in the drill-pipe direction relative to the housing, so that it can be moved down separately from the housing as soon as the front end of the housing encounters a layer of hard rock.
From the AT-PS 379 863 a drill-pipe is known, which for the guiding in the drill hole comprises a guide sleeve that partly radially surrounds the drill-pipe, the outside diameter of which guide sleeve corresponds approximately to that of the advancing drill head.
It is the objective of the invention to develop further a process and an apparatus for sinking drill holes, in particular exploration and extraction drill holes, of the described type in such a way that a deposit can mined through less hard rock layers up to the generally rocky primary rock located underneath, without in this case the process becoming uneconomical. Furthermore the apparatus should stand out by an adaptability to the most varying drilling conditions and depths and require the lowest possible production costs.
This problem associated with the process is solved by the subject of claim 1.
According to the invention, a drill-pipe which at its end facing the floor to be mined is provided with a guide point fixed in the longitudinal direction of the drill pipe, is lowered to the place where the drill hole is to be made. When doing so, normally the guide point will penetrate at least slightly into the sediment layer. Next a drill head, which on its side facing the floor has at least on cutting element that can be moved in the longitudinal direction of the drill pipe between a top position, in which the guide point projects beyond the at least one cutting element, and a bottom position in which the at least one cutting element is positioned at the same height as the end of the guide point or projects beyond same in the operating direction, is moved from its top position assumed during the lowering of the drill pipe into its bottom position. Seeing that the guide point has penetrated by a certain amount into the sediment layer, the at least one cutting element of the drill head produces in the sediment layer a drill hole start which will guide the drill head laterally before the guide point assumes a decreasing laterally guiding effect of the drill head. When the drill head penetrates further into the sediment layer, the at least one cutting element is, therefore, positioned on the same plane as the end of the guide point or even moves ahead of same, so that according to the invention drill holes up to the bedrock located underneath the sediment layer can be made without any problems. Seeing that as a rule during the drilling operation the guide point need not penetrate into the rock layer located underneath the sediment layer, its wear is reduced considerably.
With a first variant of the process according to the invention, during the drilling operation the drill pipe is made to rotate around its longitudinal axis and as a result thereof, both the drill head fixed rotationally rigid to the drill pipe and also the guide point fixed rotationally rigid to the drill pipe and also the guide point fixed rotationally rigid to the drill pipe, are made to rotate. With this variant of the process, therefor, a xe2x80x9cdrillingxe2x80x9d of the guide point into the sediment layer takes place.
It may, however, also be advantageous, to drive the drill pipe and to transmit the turning momentum to the rotationally fixed drill head, but not to the guide point which is mounted rotating around the longitudinal axis of the drill pipe. This ensures that the guide point does not rotate in the sediment. It is true that as a result thereof no drilling of the guide point into the sediment layer takes place, but it was found that in many cases an adequate guiding function of the guide point is obtained when it is pushed over a short length into the sediment layer exclusively by the mass bearing on it. As no relative movement takes place between the sediment layer and the guide point, the guide point is subjected to less wear compared to the aforementioned variant of the process according to the invention.
Particularly advantageous is the further development of the process with which the drill pipe is mounted rotationally rigid and the drill head is made to rotate relative to the longitudinal axis of the drill pipe, as by this measure the drive unit normally provided on the side of the drill pipe opposite the drill head side as well as possible complicated rotary transmission lead-throughs can be dispensed with. In this case it is possible to arrange the guide point rotationally rigid on the drill pipe.
However, in the case of a relatively hard sediment layer it may be advantageous to arrange the guide point rotating around the longitudinal axis of the drill pipe and to make it rotate around it longitudinal axis together with the drill head, as this permits a xe2x80x9cdrillingxe2x80x9d of the guide point into the sediment layer in order to increase the initial guiding effect.
In another, particularly preferred variant of the process the guide point is again mounted rotating around the longitudinal axis of the drill pipe, but is only taken along by the drill head when the latter, coming from its top position, assumes a position in which the at least one cutting element of the drill head has at least approximately reached the height of the end of the guide point.
This measure ensures that the guide point, as long as it ensures the guiding of the drill head and cannot penetrate further into the sediment layer, is not subjected to wear caused by an idle rotating in the sediment layer, but when the drill head penetrates deeper into the sediment layer it reliable prevents the formation of a xe2x80x9ccorexe2x80x9d in the area not covered by the at least one cutting element.
With a particularly preferred embodiment of the process the force with which the front end of the drill head rests against the floor to be mined or the drill hole bottom, can be adjusted by at least one buoyancy body provided on the drill head.
The design problem is solved by the apparatus disclosed in claim 8 in that on the end of the drill pipe facing the floor to be mined or the front end of the drill hole, a guide point fixed in the longitudinal direction of same is fastened, and that the drill head can be moved in the longitudinal direction of the drill pipe between a top position, in which the guide point projects beyond the at least one cutting element, and a bottom position in which the at least one cutting element is positioned at the same height as the end of the guide point or projects beyond same in the operating direction of the drill head. With the apparatus according to the invention the guide point, therefore, in the first instance serves to prevent a moving sideways of the drill head when starting the drilling, whereas after the drill head has been lowered relative to the drill pipe to behind the plane defined by the at least one cutting element, it lags behind and cannot obstruct the drilling operation by impacting on a rock base or rocky inclusions as caused by a moving ahead.
With the apparatus according to the invention it is possible to make the drill head rotate in the known manner in that the one end of the drill pipe is mounted rotating around its longitudinal axis and the use of a power-driven rotary head, which in the area of this end cooperate with the drill pipe, is provided. In this case the drill head must be arranged rotationally rigid on the drill pipe.
As in many cases, to guide the drill head it will suffice when at the beginning of the drilling operation the guide point is just pushed into the sediment layer, to reduce the wear of the guide point it may be advantageous to mount it on the drill pipe rotating around the longitudinal axis of same.
However, it is particularly advantageous when the end of the drill pipe facing away from the drill head it mounted rotationally rigid on the installation for mounting the drill pipe.
Particularly suitable for such a mounting is a cardanic suspension.
In this case the drill head is preferably made to rotate relative to the drill pipe around the longitudinal axis of the latter by means of a drive unit provided for same.
The drive unit advantageously comprises a rotary motor which cooperates with a device arranged on the drill pipe for receiving a turning momentum, which is provided preferable in the form of longitudinal teething.
The rotary motor may be a hydraulic motor.
However, it is also possible to use an electric motor as the rotary motor.
Tests have shown that in certain sediment layers the guiding effect of the guide point is sufficient when, without it rotating around its longitudinal axis, it is just pushed into the sediment layer, but other sediment layers require a rotating of the guide point around it longitudinal axis. It, therefore, is advantageous, to mount the guide point on the drill pipe rotating around the longitudinal axis of same and to provide on the guide point entrainers which can be made to engage with counter-entrainers provided on the drill head.
Preferably the entrainers and counter-entrainers consist, in the case of the entraining of the guide point, of longitudinal teeth that engage into one another.
It was found, however, that for sediment layers an embodiment of the apparatus is very suitable, with which the entrainers and counter-entrainers engage independent of the position of the drill head, related to the longitudinal direction of the drill pipe.
Particularly suitable for other sediment layers, however, is an apparatus where the entrainers and/or the counter-entrainers are designed in such a way that the guide point is only engaged with the rotating drill head when the at least one cutting element is positioned at the same height as the end of the guide point or projects beyond same in the operating direction of the drill head. This measure ensures that a further lowering of the drill head into the sediment layer is not prevented by a xe2x80x9ccorexe2x80x9d formed in the area not covered by the at least one cutting too.
In a preferred embodiment the longitudinal teething forming the entrainers and counter-entrainers is provided only on the bottom part of the guide point, the counter-teething only in the upper part of the drill head, in such a way that when the drill head is moved along the drill pipe in the direction of the guide point, the upper end of the teething engages with the bottom and of the counter-teething when the at one cutting element has nearly reached the height of the end with the guidepoint.
A particularly good adaptability of the apparatus to different sediment layers is obtained when at least one buoyancy body is provided on the drill head for adjusting the drilling force acting in the operating direction of the drill head. By this measure the drilling force acting in the operating direction of the drill head can adapted to the properties of the sediment layer in question, without causing a change in the force with which the guide point is pushed against the sediment layer. Thus it is possible, in particular in the case of very hard sediment layers, to press the guide point into the layer with great force so as to achieve an adequate guiding effect, but at the same time to regulate the drilling force in such a way that the engaging of the at least one cutting element does not cause a slipping sideways of the drill hole, whereas on the other hand an optimum drilling progress is achieved.
When the at least one buoyancy body comprises a tank which optionally can flooded or filled with a gas, preferable compressed air, then the drilling force can also be changed during the drilling operation. As a result it is possible, for example, to choose at the beginning of the drilling operationxe2x80x94as long as there still exists the risk of a xe2x80x9cdriftingxe2x80x9d of the drill holexe2x80x94a lower drilling force, but to increase the drilling force so as to increase the drilling progress as soon as the drilling tool begins to guide itself in the drill hole.
The apparatus according to the invention is preferably used in conjunction with a floating platform for sinking drill holes in the ocean floor, on which platform the end of the drill pipe opposite the drill head end is mounted.
In that case it is particularly advantageous, in order to compensate vertical movements of the platform caused by the ocean swell or tide lift, to split the drill pipe into an upper drill pipe part mounted on the platform and a bottom drill pipe part on which the drill head and the guide point are mounted, wherein the upper and the bottom drill pipe parts engage into one another telescopically in the longitudinal direction of the drill pipe and can be moved relative to one another in such a way that the vertical movement of the platform are compensated without the drilling force experiencing a significant change.
With a preferred embodiment of the apparatus according to the invention, a length-variable force generator, preferably a piston/cylinder unit is provided which is mounted on the one side on the bottom drill pipe part, on the other side on the drill head and with which the length variation takes place in the direction of the longitudinal axis of the drill pipe. By this measure the drill head can be moved relative to the bottom part of the drill pipe without this requiring an activation of the winch provided on the platform and a stressing of the ropes. This is especially advantageous when the drill head is xe2x80x9cjammedxe2x80x9d in the drill hole, e.g. due to a collapsing of the drill hole walls, seeing that by a corresponding activating of the length-variable force generator the drill head can be moved upwards relative to the guide point which, especially when the drill hole extends through the entire sediment layer, rests on the hard bedrock located underneath. In most cases the drill head can, therefore, also be loosened after a collapsing of the drill hole walls.
This embodiment furthermore makes it possible to adapt the projecting length of the guide point to the conditions corresponding to the properties of the floor.
If on the bottom drill pipe part, preferably near its upper end, at least one buoyancy body is provided, the buoyancy force of which can be controlled, then the force with which the guide point rests on the floor can be adapted to the prevailing conditions. If in this case the drill head is provided with a length-variable force generator, then the drilling force can be increased by the proportionate mass force of the bottom drill pipe part and of the components attached thereto in the axial direction.